An aircraft's air data system measures outside air pressure to provide, for example, airspeed and altitude data to cockpit instruments.
Typically, air data systems use pressure sensors comprising forward (pitot) and side-facing (static) orifices on the surface of the aircraft. These orifices are linked to cockpit gauges, or pressure transducers, via small-diameter pneumatic tubing.
This tubing may become blocked with water or debris. Such blockages are particularly problematical (for example, blockages may result in erroneous cockpit indications) and have resulted in, or been suspected as causing, aircraft losses.
Conventionally, to avoid or alleviate a problem of tube blockages, tubing runs are designed to provide positive drainage of water or otherwise designed to be least affected by moisture or other foreign matter. Also, ‘drain traps’ may be installed at the lowest points in the pitot-static lines to permit the removal of collected water.
Protective ‘Remove Before Flight’ covers are normally fitted over an aircraft's pitot-static sensors, when the aircraft is on the ground, to prevent water, solid debris, or insects, from blocking the orifices or tubing.
However, if tube blockages do occur, or are suspected, the pitot-static system pneumatic lines may have to be dismantled to permit cleaning. This tube cleaning could be performed by blowing, suction, flushing out with a fluid, or the insertion of a probe.
This dismantling and cleaning process may be time-consuming. Also, it may be required that, once re-assembled, the pitot-static system must be tested for air leaks.